[ RadSafe ] RE: Looking for References on Liquid Scintillation Counting for Tritium

[Dimiter Popoff]

 Felipe,

>  2.  Are there techniques for eliminating CL interference at low count
>  rates (a few CPM above background)?

Since they all use photomultiplyer tubes, your only bet would be some sort
of light intensity based discrimination, if the difference is present in the
signal. I don't know whether commercial lsc devices do this (I am sure Franz can
shed more light on that), but it is no rocket science to do, should be
doable one way or the other.
 However, I would think twice if not more about the actual availability of
a signal to go after (i.e. whether there is _some_ difference between
the light pulses because of the causing phenomeon), I have no clue here.

Dimiter


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-------Original Message-------
> From: Felipe Gaitan <gaitan at impulsedevices.com>
> Subject: RE: [ RadSafe ] Looking for References on Liquid Scintillation	Counting for Tritium
> Sent: Sep 06 '05 22:26
> 
>  Gentlemen,
>  
>  Thank you Alex, Franz and Bob for your response.  I'm writing to the
>  list in case other people are interested but we could communicate off
>  line if you prefer.
>  
>  So far the consensus is that there are no definite references due to
>  the fast pace of development and that the two main categories are
>  high and low count rates.  So it looks like I need to give more
>  details about our particular application.
>  
>  We are trying to replicate an experiment done at Oak Ridge (and more
>  recently at Purdue) in which the authors claim to be producing
>  Tritium in deuterated acetone using acoustic cavitation.
>  
>  Here is a summary of what I consider are the relevant parameters (let
>  me know if you think I'm missing any):
>  
>  1.  Sample liquid:  both regular and deuterated acetone.  According
>  to the authors, the tritium backgrounds for regular and deuterated
>  acetone are about 20 CPM and 50 CPM respectively. Deuterated acetone
>  has a higher background due to tritium contamination (I assume during
>  the deuteration process).  As far as I know, they have used regular
>  (not super-low background) LS counters (Beckman LS6500, I believe)
>  
>  2.  They measure anywhere between 2-15 CPM above background for the
>  deuterated acetone (none for the other control samples including
>  regular acetone)
>  
>  3.  I'm aware that chemiluminescence (CL) and other types of
>  luminescence can interfere with tritium measurements and I don't know
>  if or how the authors compensated for it. I wouldn't be surprised if
>  acoustic irradiation could excite some molecules and cause them to
>  emit photons. I don't think the regular machines can compensate for
>  CL when the count rate is that low (right?).  The only way I know is
>  to monitor the count rate (both coincident and non-coincident) as a
>  function of time.
>  
>  Here are my questions:
>  
>  1.  Do you know anybody measuring low levels of tritium is acetone
>  samples? I'm wondering if there are particular issues with acetone.
>  
>  2.  Are there techniques for eliminating CL interference at low count
>  rates (a few CPM above background)?
>  
>  3.  What other effects can interfere with this kind of measurements?
>  
>  Thanks in advance,
>  
>  Felipe
>  
>  --
>  D. Felipe Gaitan, Ph.D.
>  Chief Scientific Officer
>  Impulse Devices, Inc.
>  13366 Grass Valley Av.  Unit H
>  Grass Valley, CA  95945
>  Phone: 530-273-6500 Ext. 112
>  Fax:  806-498-6731
>  
>  email: gaitan at impulsedevices.com
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-------Original Message-------